1. Field of the Invention
This invention relates to lighting devices and light sources, and in particular, it relates to control and tuning techniques for light sources, and tuning of the output light color.
2. Description of the Related Art
Currently, light sources for high power stage lighting devices primarily use metal halide discharge lamps. Metal halide discharge lamps are which light sources, and their life is relatively short, from a few hundred to a few thousand hours. Because the emission spectrum of metal halide discharge lamps is a white continuous spectrum, output lights of different colors can only be obtained by using color filters. The color patterns projected by such lighting devices have relatively low color saturation; the color is neither vivid nor rich.
To increase the color saturation of monochromatic output light, conventional stage lighting devices sometimes use very narrow band color filters. Although the color saturation is increased, the brightness of the output monochromatic light is reduced.
With the development of solid state light source technologies, solid state light sources, in particular light emitting diodes (LED), are becoming more widely used in state lighting systems. But because of the limitations in heat dissipation and light flux of LED lights, currently, LED light sources are mainly used in low-end low power color changing light products.
To use solid state light sources in high power stage lighting devices, a device described in a patent application previously filed by the same applicant (see FIG. 1) utilizes multiple high power LED arrays to provide red (R), green (G) and blue (B) lights separately, and utilizes light combining devices such as an X-shaped light combiner 15 to combined the lights and obtain output lights of desired colors.
In addition, current light source devices use a single light source in combination with phosphor materials to generate output light of various colors. For example, Chinese patent application No. 2008100653661 describes a device which employs a moving unit disposed on the optical path of a light source, the moving unit carrying multiple phosphor materials and rotating at a high speed, to generate an output light which is a mixture of multiple monochromatic lights. This device can also control and adjust the output power of the light source in real time to achieve desired color variation of the combined output light.
A shortcoming of the above technology is that, in the abovementioned technology by the same applicant, although the high power stage lighting device can achieve high brightness and high saturation monochromatic light, the color rendering capability of the white light is still insufficient. The reason is as follows. Conventional metal halide discharge lamps are hot light sources whose light emitting efficiency is not affected by the output power. For example, a 575 W lamp, whether its output flux is 49000 lumen or 110000 lumen, the light emitting efficiency is 85 lumen/W for metal halide discharge lamps. To the contrary, the light emitting efficiency of current high power LED decreases with increased drive power. Moreover, in current R, G, B base color LEDs, green LEDs have the lowest light emitting efficiency and blue LEDs have the highest light emitting efficiency. However, because the white spectrum contains the most green component and the least blue component, to obtain adequate white balance, the brightness of the white LED stage lighting device will be low. In particular, a stage light requires a low color temperature light (e.g. 3200K) in sometimes applications, which requires even more green light components, resulting in even lower brightness of the white light. Further, the above described light source uses large arrays of high power LEDs, which increases the cost of the light source compared to conventional devices and limits its applicability.
Although the light source device described in the above mentioned Chinese patent application No. 2008100653661 can provide rich color variation, it requires high rotation speed of the moving unit to achieve desired color adjustment, which imposes high requirement on the real time control of the light source.